Hydraulics in mining: safe and reliable

Eliminating downtime and ensuring safety in mining — two benefits hydraulics provides consistently.

Josh Cosford • Contributing Editor

More than almost any other industry appropriati ng fl uid power, mining is where safety sits front and center from design to executi on. Surface mining enjoys bragging rights to some of the most massive machines ever manufactured by humans. Vehicles of downright monstrous proportions possess the power to smatter a pickup truck as easily as a thumb smears a tiny red clover mite crawling up your patio furniture. Despite the destructive capacity of surface mining machinery, underground mining sits at the head of the boardroom table of jeopardy.

Image courtesy of iStockphoto.com

Hundreds of lost lives result from single, horrific accidents, especially related to underground explosions. For as long as we have been mining, we have been sacrificing lives to feed the world’s industrial and commercial machines. Miners are unsung heroes with next level bravery, and these heroes must never go unrecognized.

With what we’ve learned in the past few hundred years, I’d like to say miners are now perfectly safe. Sadly, large scale disasters happen in mining, but that doesn’t mean we haven’t made huge strides in caring for our valuable human resources. Much of what the mining industry focuses on is indeed safety. Track record or not, the mining industry as a whole is committed to protecting important lives. If new technology, techniques and temperament combine to save even one life, that’s a step in the right direction.

For generations, fluid power has been the top choice for underground mining machinery for various reasons. One of the most important has been its strictly hydro-mechanical operation, previous to the more recent electrical or electronic control. When fluid is transmitted under pressure to achieve work, no electrons are required to activate valves or actuators. No electrons mean no spark. No spark means no ignition source.

Since the beginning of mine safety awareness, the potential has always been there to create a spark that could ignite methane or subsequently, coal dust. Direct ignition of coal dust is rare, especially with our current mindfulness of safety, but when methane first ignites, the high energy provides the potential to ignite coal dust.

Hydraulic clutch cylinders from Higginson Equipment, undergo a rigorous testing and manufacturing regimen to ensure they meet the safety requirements in mining hoists.

A hydrostatically driven mine vehicle using only hand- and foot-operated valves to operate requires absolutely zero electricity. Buckets, conveyors, drills and other machinery need not require a single electrical component aside from the engine’s electric ignition and lighting. The old school hydraulic machines kept miners safe for many generations before electronic control was developed to resist and avoid any contribution to spark or explosions. These days, electronic control systems are prolific in mines, but the bulk of the work is still hydraulic in nature.

Hydraulics are critical to the safe operation of many machines in a mine. High power density, inherent controllability, and mature technology make hydraulics a safe choice to control machinery. One category of machinery often overlooked for its need for hydraulics’ benefits is mine hoists tasked with hauling persons and machinery the vast depths underground. Mine hoists are advanced machines employing hydraulics on essential functions such as the brake and clutch.

A hoist (or elevator) carries not only ore and machinery but also precious human cargo. In fact, some hoists lower and lift hundreds of persons more than two miles (three kilometers) into the dark depths. Although they travel at high velocity, hoists must move smoothly and safely. A sudden surge in either direction results in startled miners at best or various injuries at worst.

Hydraulics are critical to the safe operation of many machines in a mine. High power density, inherent controllability, and mature technology make hydraulics a safe and reliable choice to control machinery.

So easily controlled is fluid power that proportional control over the pressure and velocity of braking systems is guaranteed. Multiple, redundantly controlled brakes ensure the hoist stops and starts smoothly, and the parallel nature of the valves provides many backup channels should one valve fail. Accumulators plumbed into the primary supply secure an emergency supply of hydraulic energy should both of the pumps somehow fail simultaneously or if power unit electrical supply is lost altogether.

The extensive quality control measures to manufacture mine-ready hydraulic components may be shocking to the average person. Valves, for example, must be produced to high standards meeting one of the various criteria set out by international bodies such as CSA, UL, and IEC, etc. Components must be explosion-proof, intrinsically safe, control reliable, and manufactured from high-quality raw materials.

An explosion-proof component as defined in the National Electric Code dictates that “an enclosure must be able to contain any explosion originating within its housing and prevent sparks from within its housing from igniting vapors, gases, dust, or fibers in the air surrounding it. Therefore, explosion-proof, when referring to electrical enclosures, does not mean that it is able to withstand an exterior explosion. Instead, it is the enclosure’s ability to prevent an internal spark or explosion from causing a much larger blast.”

UL or CSA rated control valves must be tested in the respective authority lab. Depending on the nature of the component being tested, it may need to operate reliably for a million cycles before it’s given the stamp of approval. Pressure tests may confirm the rated pressure, and if necessary, destructive testing may evaluate the burst pressure meets expectations.

Accumulators are used frequently in mining, for example, so checking to see that burst pressure is indeed at least four times working pressure will prevent failure or injury down the road.

Accumulators are used in mining hoists to supply emergency hydraulic energy should both of the pumps somehow fail simultaneously or if power unit electrical supply is lost altogether. Image courtesy of Roth Hydraulics

It’s not good enough that mines only use high quality valves manufactured within the scope of various safety standards, but actuators must also represent the best of what’s available. Off-the-shelf hydraulic cylinders need not apply since their quality cannot be guaranteed without strict quality control measures implemented at every step of manufacture.

Our team here at Higginson Equipment, where I work, can attest to the mining industry’s heightened prerequisite for quality. We manufacture hydraulic clutch cylinders for mine industry applications. Starting with high-quality alloys (such as 4140 for the heads and caps), we must send the raw material to third party firms for non-destructive testing before any chips fly in the machining process. Ultrasonic testing confirms the quality of the grain structure conforms to strict ASME and/or ASTM standards, and then the report is added to our quality package later provided to the customer.

The strict quality control doesn’t stop at the raw material. Critical components must be tested again after manufacturing. The machined piston rod pays a visit to the NDT lab once again to be examined via the magnetic particle test (or sometimes die penetrant test) to confirm the machining process left the material free from cracks, flaws, inclusions or lap-type defects. The threads must be perfect on both the piston and attachment end. Any such cracks or defects, however small, could be catastrophic when subjected to the extreme forces applied by pressurized oil.

Upon assembly of machined parts, we perform dimensional checks on up to 20 critical surfaces, threads, and envelopes, all before we consider sending the quality control package to the customer. Upon approval of documents, our customer sends one of their senior quality inspectors to double-check the finished product. This is the final step in a long process to ensure valuable human lives and other capital are safe in the hands of a machine such as a mine hoist.

Source: (https://www.specificsystems.com/common-questions/what-does-explosion-proof-mean)